linux-kernel - Re: workqueue code needing preemption disabled

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Message-ID: <20130318164351.GA21516@mtj.dyndns.org>
Date:	Mon, 18 Mar 2013 09:43:51 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	RT <linux-rt-users@...r.kernel.org>,
	Clark Williams <clark@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: workqueue code needing preemption disabled

Hello, Steven.

On Mon, Mar 18, 2013 at 12:30:43PM -0400, Steven Rostedt wrote:
> If you happen to know the critical areas that require preemption to be
> disabled for real, we can encapsulate them with:
> 
> 	preempt_disable_rt();
> 
> 	preempt_enable_rt();
> 
> These are currently only in the -rt patch, but it annotates locations
> that require preemption to be disabled even when -rt converts spin_locks
> into mutexes. These obviously can not contain spin_locks() as
> spin_locks() can block and schedule out.

Making gcwq locks disable preemption would be much safer / easier, but
if that's not desirable, anything touching gcwq->idle_list would be a
good place to start - worker_enter_idle() and worker_leave_idle().
Hmmm... ignoring CPU hotplug, I think those two might just do it.
Give it a try?  How reproducible is the problem?

Thanks.

-- 
tejun
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